When a hard disk drive (HDD) fails to be accessed for a long time or power supply is temporarily broken, rotation of a magnetic disk is stopped, that is, the magnetic disk is “spun down”. At the time when an HDD is spun down, when a control device transmits to the HDD a command for requesting it to be spun up, operation of the HDD is restored.
On the other hand, as a control technology at the time when a malfunction occurs in a storage device such as an HDD, the following technology is used. Examples of the control technology includes a control device which is connected to a plurality of HDDs and a storage device including a voltage monitoring function of a power supply line to the HDDs, when reduction in a voltage of the power supply line is detected, temporarily breaks a data line to the storage device, and transmits a start-up command to the HDDs after voltage restoration.
Further, as another example, there is used a control device which, when detecting reduction in a DC voltage supplied to an HDD, stores power supply failure information in redundant arrays of inexpensive disks (RAID) configuration information as well as interrupts reading and writing in the HDD and, when detecting restoration of the DC voltage, releases the power supply failure information from the RAID configuration information as well as resumes the reading and writing in the HDD.
In addition, as another example, there is used a control device which classifies each disk belonging to a RAID group into multiple categories for each RAID group as a closure determination object every time an event to determine whether to close the RAID occurs in a RAID device, and based on a count result of the number of corresponding disks in units of classifications, determines whether to close the RAID group.
Japanese Laid-open Patent Publication No. 2006-133926
Japanese Laid-open Patent Publication No. 2007-122263
Japanese Laid-open Patent Publication No. 2007-304728
Incidentally, in a storage system, a plurality of HDDs may be connected to a control device. The storage system including the plurality of HDDs is configured so that spun down HDDs may be restored under the control of the control device. In the above case, when the plurality of HDDs are spun down at one time, a processing load of the control device increases because of restoration processing of the HDDs. When the processing load of the control device increases because of the restoration processing of the spun down HDDs, access processing to HDDs which are not spun down grows stagnant. Alternatively, the time necessary for restoring each of the spun down HDDs becomes longer.